The present invention relates to an interrupt control circuit and, more particularly, to a circuit for detecting the abnormal state of a circuit for generating an interrupt.
There has been known an information processing apparatus comprising a CPU (central processing unit) and having an interrupt control circuit for suspending a process being executed and causing an interrupt processing program (interrupt handler) having a higher priority to be executed. U.S. Pat. No. 5,423,049 discloses one example of a circuit that controls, with the use of a timer, interrupt requests to the CPU which request such interrupt processing.
There has also been a system program in which an interrupt generation circuit periodically generates an interrupt request and a CPU performs a process in response to the interrupt, thereby allowing a normal system operation to be continued. When the periodic interrupt requests are no more generated from the interrupt generation circuit, the normal system operation cannot be continued any more so that the CPU is required to detect the abnormal state and perform error handling.
For this purpose, an interrupt control circuit has used a timer interrupt as means for detecting that the interrupt requests are no more generated from the interrupt generation circuit. That is, timer interrupts are generated at a time interval at which interrupt requests are supposed to be generated and it is checked in a timer interrupt handler whether or not the interrupt requests are generated from the interrupt generation circuit. When the interrupt requests are not generated from the interrupt generation circuit, the abnormal state of the system is detected so that error handling is performed.
However, such a method has had a problem that timer interrupts need to be repeatedly performed for error detection and, accordingly, resources cannot be used efficiently. In addition, the method also has had the problem that, even when the state of the system is normal, the processing ability of the system program deteriorates since it is necessary to perform the process of the timer interrupt.